Sized paper product, size and method of making the same



United States Patent SIZED PAPER PRODUCT, SIZE AND METHOD 6F MAKING THE SAME Charles J. Prescott, In, Nor-wood, Mass, assignor to Bennett Incorporated, Cambridge, Mass, a corporation of Massachusetts N0 Drawing. Application December 28, 1951, Serial No. 263,996

3 Claims. (Cl. 106-230) This is a continuation of my copending application Serial No. 35,065, filed June 24, 1948.

The object of my invention is to utilize the waste liquor resulting from the manufacture of cellulose by the so-called sulfite process in which wood or other fibrous plants are cooked under pressure with a solution containing sulphurous acid and a base such as lime or magnesia. For example, in the manufacture of paper pulp by the sulfite process, wood chips are heated in a digester with a solution of calcium bisulfite including a certain amount of free sulfurous acid until the non-cellulosic constituents of the wood are dissolved. The liquid containing the extracted bodies is then drawn off leaving relatively pure cellulose. This liquid is obtained in large quantities as a more or less undesirable by-product, and is commonly referred to as waste sulfite liquor.

The exact chemical nature of waste sulfite liquor is not fully understood, and will vary somewhat depending on the particular wood as well as the composition of the original sulfite solution used in digesting the pulp. It consists essentially of complex organic derivatives from lignin, and includes in addition various gums, tannins, acids, sugars, and inorganic impurities. The waste sulfite liquor as recovered from the digester is a thin amber colored solution containing approximately 10% solids, and having a pH of 3.5 to 4.5.

I have discovered that this waste liquor can be used very effectively to prepare dispersions of water-immiscible bodies which when incorporated in paper making stock and then fixed on the fibres by the subsequent addition of alum or other similar electrolyte will give highly satisfactory sizing results. In this manner, an undesirable by-product from the manufacture of paper pulp which has heretofore been considered of little value, if not an actual nuisance, can be utilized by paper mills themselves in the production of papers or boards that are resistant to the penetration of water and will show a low moisture absorption test.

The use of waste sulfite liquor in connection with paper sizing has been proposed before but as far as I am aware only in a manner entirely dilferent from the present invention.

In accordance with my invention, I use Waste sulfite liquor to form an aqueous dispersion or emulsion of normally solid thermoplastic hydrocarbon wax, especially paraffin wax, which dispersed material is then incorporated in paper stock preparatory to sheeting the stock on a paper making machine and fixed on the stock by the addition thereto of aluminum sulfate or other equivalent mordant salt or electrolyte.

For this purpose I prefer to use the dilute raw waste sulfite liquor exactly as it is recovered from the digester, without any further treatment whatsover such as neutralization, purification, evaporation or concentration. This means a substantial saving of expense since it completely eliminates the cost of having to add any chemicals, or of concentrating and drying the liquor. Furthermore, I have found that the raw dilute waste sulfite liquor, at approximately 10% solids, produces dispersions or emulsions that are particularly well suited for paper sizing, and which will give better results than dispersions or emulsions made from waste sulfite liquor which has been first concentrated or dried in powder form and then redissolved, or has been neutralized or subjected to other chemical reactions. The heat employed to concentrate or evaporate the raw waste sulfite liquor causes decomposition of some of the complex organic bodies, and thus destroys to a certain extent the colloidal properties of the material. If the waste sulfite liquor is not concentrated or evaporated, the maximum emulsifying eflfect is retained, and it is not necessary to use any additional stabilizers to protect the. dispersion. Evaporation also results in a very dark color which is undesirable especially if the size is going to be used in light colored papers or paper boards. The color of the dilute raw waste sulfite liquor on the other hand is pale amber, and dispersions or emulsions prepared therefrom will not affect the whiteness of the finished paper any more than the ordinary type of cooked rosin size.

Chemical treatment is likely to be equally detrimental to the dispersing and emulsifying properties of the raw waste sulfite liquor. For the purpose of sizing paper it is advantageous to produce a dispersion or emulsion which will remain permanently stable under as wide a range of operating conditions as possible in orderto avoid difiiculties on the paper machine caused by premature coagulation or agglomeration of the size. The chemical nature of the dilute raw waste sulfite liquor as it comes directly from the digester is such that dispersions or emulsions prepared therefrom in accordance with the method of this invention are exceptionally stable, not only in the presence of hard water containing calcium salts or other similar electrolytes, but also at any temperature which would be normally employed in handling paper stock, and this stability is not affected by any degree of acidity in the stock, all of which conditions are often encountered in paper making practice. If the dilute waste sulfite liquor is neutralized by the addition of alkali, this reduces the acid stability of the dispersions or emulsions subsequently made from the treated liquor since the alkali present will react with any saponifiable materials either in the waste sulfite liquor itself or in the water immiscible bodies to. be dispersed, forming soaps which will readily precipitate under acid conditions, thus coagulating or breaking the dispersion or emulsion. Therefore, it is desirable to avoid treatment of the dilute waste sulfite liquor with any chemicals capable of forming such a reaction.

I shall now describe a typical and preferred dispersion for the purposes of this invention and the method of producing said dispersion. A tank equipped with suitable heating facilities, such as a steam jacket or steam coil, is loaded with 300 parts by weight of a hydrocarbon wax, for instance parafiin wax with a melting point of about 128 -l30 F. and 200 parts by weight of natural rosin, for instance the grade known as F gum rosin. The

mixture is melted and heated to a temperature of F., whereupon it is added to 500 parts by weight of dilute waste sulfite liquor having approximately 10% solids concentration, which has been heated in a separate tank to about 180 F. By so heating the wax mixture to a temperature well above its melting point, the viscosity of its constituents is lowered and since the temperature as given herein is above the boiling point of water, as soon as the hot wax mixture is added to the sulfite liquor a portion of the water content of the latter is flashed into steam, producing agitation of the mixture. Both of these actions aid in producing the desired dispersion. The temperature to which the wax mixture is heated is not critical, however, but it should be kept below its decomposition point. Likewise the temperature to which the sulfite liquor is heated is not critical, though the use of hot liquor aids in producing the desired fine dispersion. This combination is intimately mixed for a few minutes by a rapidly revolving propeller blade, or other adequate means of agitation, and is then emulsified by passing the melted mixture and the dilute waste sulfite liquor solution through a dispersion machine, colloid mill, homogenizer, or other similar apparatus. The temperature of the resulting dispersion will run from 180-190 F., and the solids content Will be approximately 55%. This is preferably diluted with cold water to a concentration of 2%3% before use in sizing paper.

The dispersion produced as hereinbefore described is an acid stabilized suspension of normally solid thermoplastic water-immiscible materials in an aqueous medium, having a pH of around 4.5 to 5.5. The size of the particles is extremely small, averaging 1 micron to 3 microns, and the emulsion may be kept indefinitely without any substantial separation of the dispersed solids. The dispersion is further characterized by the complete absence of any saponified or precipitated soaps; the rosin content of the mixture, for example, is wholly unsaponified and is present only in its natural state, or as so-called free rosin.

The dispersion may be used very successfully as a beater size or it may be added continuously to the paper stock at some later stage in the paper making cycle with equally satisfactory results. In either case, a sufiicient quantity of aluminum sulfate or other electrolyte is subsequently employed to fix or set the size onto the fibres and thus insure proper retention and distribution of the waterproofing material in the finished paper or paper board; The amount of size which may be added to the paper stock will depend on the degree of waterproofing or sizing needed in the finished product. Usually from 1% to 3% of the dispersion solids based on the dry weight of the fibre will give the required sizing results.

Whereas I have described in detail a preferred embodiment of my invention, it is to be understood that the principles of the invention may be employed in a wide variety of practices or products. For instance, the amount of hydrocarbon wax in the dispersed mixture may be changed to any proportion desired. In the example hereinbefore described, the ratio was 60 parts of wax to 40 parts of rosin. The reverse ratio of 40 parts of wax to 60 parts of resin can also be used. For certain purposes the rosin may be eliminated completely from the mixture, in which case the dispersed solids will consist entirely of wax. The amount of waste sulfite liquor used may vary in accordance with other changes in the formulation. While the dilute raw waste sulfite liquor exactly as it is recovered from the digester is preferred for the reasons mentioned herein, a solution made by redissolving concentrated or dried waste sulfite liquor can also be employed in some cases if necessary. In fixing the dispersed solids on the paper making fibres, it is possible to use besides aluminum sulfate any of the salts or electrolytes commonly employed in connection 4 with paper making as, for example, aluminum chloride, sodium aluminate, ferric sulphate and the like.

The dispersions herein described may be used to size all kinds of fibrous materials or paper making stocks, including rag pulps, wood pulps, asbestos fibres, wood fibres, or mixtures of such fibres, which may be formed into various grades of papers and paper boards including light weight papers, heavy papers, box boards used for making containers and cartons and low density boards such as those used for sheathing or insulating purposes.

I claim:

1. The method of preparing acid-stable, soap-free sizing compositions, which comprises associating normally solid thermoplastic hydrocarbon wax and natural resin in molten condition with aqueous waste sulfite liquor, and bringing about the formation of an oil-in-water type of dispersion having a pH in the neighborhood of 4.5 to 5.5.

2. An acid-stable, soap-free sizing composition adapted to be incorporated into paper stock and to be fixed on the fibres of said stock, for sizing efiect, by the addition of an electrolyte; said composition comprising a dispersion of the oil-in-water type wherein the dispersed phase comprises normally solid thermoplastic hydrocarbon wax and rosin, the continuous phase comprises water, and the dispersing agent is waste sulfite liquor.

3. An acid-stable, soap-free sizing composition adapted to be incorporated into paper stock and to be fixed on the fibres of said stock, for sizing effect, by the addition of an electrolyte; said composition comprising a dispersion of the oil-in-water type wherein the dispersed phase comprises from about 40 to about 60 parts of normally solid thermoplastic hydrocarbon wax and from about 60 to about 40 parts of rosin, the continuous phase comprises water, and the dispersing agent is waste sulfite liquor.

References Cited in the file of this patent I UNITED STATES PATENTS 

1. THE METHOD OF PREPARING ACID-STABLE, SOAP-FREE SIZING COMPOSITIONS, WHICH COMPRISES ASSOCIATING NORMALLY SOLID THERMOPLASTIC HYDROCARBON WAX AND NATURAL RESIN IN MOLTEN CONDITION WITH ASQUEOUS WASTE SULFITE LIQUOR, AND BRINGING ABOUT THE FORMATION OF AN OIL-IN-WATER TYPE OF DISPERSION HAVING A PH IN THE NEIGHBORHOOD OF 4.5 TO 5.5. 